Dimming Starlight

AMNH/D. Finnin

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Telescopes can easily zoom in on a star. But to see a dim object next to a star, such as a planet, astronomers need to block out the star’s light. A coronagraph attached to a telescope can eliminate nearly all the starlight, revealing dim objects nearby. With this coronagraph, researchers made the first discovery of a starlike object called a brown dwarf. Today coronagraphs are helping astronomers search for new planets.

Hidden Planets

If you looked at our Sun from a telescope 30 light years away, its light would be so bright it would obscure all the planets. Using a telescope with a coronagraph, Jupiter and Saturn would become visible.

The coronagraph in this case was attached to the 60-inch (1.5 meter) wide telescope at the Palomar Observatory in southern California. With it, researchers made the first discovery of a brown dwarf as well as several "debris disks" where planets take shape.

For Educators

Topic:
Astronomy

Subtopic:
Stars

Keywords:
Coronagraphs, Light, Astronomy, Stars, Brown dwarf stars

Audience:
General

How It Works
Inside the coronograph, a series of mirrors and lenses position and focus the light. Carefully placed disks and rings block out 98.5% of the star's light, enabling astronomers to see dim objects near the star.
Numbers correspond to labels on coronograph
1) Light enters from the telescope at top.
2) Mirror reflects light upwards (visible on back of instrument)
3) Mirror reflects light downwards
4) Reflective central disk blocks 95% of starlight
5) Outer ring and central disk block light that bends around central disk
6) Image reflected to right
7) Image reflected upwards
8) Camera receives final image
AMNH/D. Finnin